Rheostat



SePt- 15, 1931 N. c. scHELLENGER 1,823,474

RHEosTAT Filed Oct. 25, 1926 2 Sheets-Sheet ll 4 J. V n

Sept. l5, 1931. NI Q SCHELLENGER 1,823,474

RHESTAT Filed Oct. 25, 1926 2 Sheets-Sheet 2 w mllll VPatented Sept. 15, 1931 UNITED STATES PATENT OFFICE NEWTON C. SCHELLENGER, F ELKHART, INDIANA, ASSIGNOR TO CHICAGO TELEPHONE SUPPLY COMPANYhOF ELKHART, INDIANA, A CORPORATION OF DELAWARE RHEOSTAT Application led October 25, 1926. Serial No. 143,906.

k This invention has to do with current control devices such as rheostats and potentiometers. More particularly the present invention relates to improvements which I have made in rheostats of the same general characterasl that disclosed in my copending patent application, SerialrNo. 114,126 filed June 7th, 1926.

I have found that there is a demandfor a rheostat having a properly cooled resistant strip. To meet this demand I have devised a rheostat having a molded composition base provided with a corrugated outer periphery.

The corrugations insure cooling of the stripl preferably of a hollow cylindrical shape and has one end closed by a depressed o`r concave portion. vThis depressed portion is integral with the wall of the base and defines a seat for the. rlieostat contact mechanism. l Another feature of my rheostat base is the provision of novel stops for limiting the travel of the contact arm; -thestops being part of the molded product or base. Also adjacent the stops the base has formed therein seats for receiving the heads of ythe screws employed for securing the resistant strip to the base. Each of these seats is rectangular in shape and serves to lock the associated screw against rotation.

Still another feature of the invention pertains to the construction of the resilient washer associated with the contact arm of the device. The washer comprises essentially al depressedA circular plece of material providedl with a concentric circular aperture for receiving the operating shaft of the device and having a lateral extension comprising an arm equipped 'with a bifurcated end.

For purposes of simplicity in construction, I have provided a slot in the molded base for receiving the bifurcated arm of the washer; the arm being fastened to the base by one of the screws previously mentioned, thus an- Y choring the washer against rotation.

The resistance strip I employ in my present device maybe wound with wire in accordance with the features of the co-pending application of Charles Havlish, Serial No. 729,479, filed August 1, 1924.

Other Obj ects and advantaves of my invention will more fully appear from the following detailed description taken in connection with the accompanying drawings which illustrate an embodiment thereof and in which Figure 1 is an elevation of my novel device looking at it from one side;

Fig. 2 is an elevation of the device looking at it froxn'another side;

Fig. Sis a sectional view through the device illustrating the manner in which same is fastened to a mounting panel;

Fig. 4 is a fragmentary sectional view taken on substantially the line 4-4 of Fig. 3 looking in the direction indicated by the arrow;

Fig. 5 is a detail view illustrating my novel resilient washer;

Fig. 6 is a sectional view taken on substantially the line 6-6 of Fig. 5;

Fig. 7 is a view taken on the line 7--7 of Fig. 3 looking downwardly;

Fig. 8 is a sectional view taken on the line 8 8 of Fig. 3 looking in a direction indicated by the arrow;

Fig. 9 is a `fragmentary View drawn to an enlarged scale of a portion of a resistant strip embodying novel features of my invention;

Fig. 10 is a sectional view taken on the line 10-10 of Fig. 9;

Fig. 11 is a sectional view taken on the line 11-11 of Fig. 9 drawn to an enlarged scale; and

Fig. 12 is a view partly in sections taken on substantially the line 12-12 of Fig. 9 looking upwardly.

Referring now to the drawings in detail in which like reference numerals designate similar parts throughout the several views, 15 denotes generally a base. or frame member which is preferably made of molded composition, such as phenolic condensation matter. I have obtained excellent results by making the base of bakelite.

This base includes a hollow body defined by a circular wall having its outer periphery provided with a plurality of corrugations 16. At one end the base is closed by a depressed or concave portion 17 lying within the dimensions of the base. Thls depressed portion is cup-like in shape and has a substangially flat portion 18 serving as a seat for receiving the contact mechanism of the device. Located 'within the hollow 19 of the base 15 is a circular sleeve 20 which is preferably secured to the body at the time the same is molded in a manner well known to those familiar with m the phenolic condensation molding art.A yThis a reduced opening 22; an operating shaft 24 telescopes this sleeve 20 and has a reduced portion 23 extending through the reduced opening 22 in sleeve 20. Also shaft 24 has an annular shoulder 25 which abuts a portion of the sleeve 20 defining the opening 22 as shown in Fig. 3. Threaded into'the sleeve 2O and surrounding the shaft 24 is a thimble 27 extending through an aperture 28 in a mounting panel 30. The thimble 27 has a polygonal shaped head 29 which abuts a washer 31 surrounding the threaded portion of the thimble. This thimble 27 serves to securely clamp the base 15 to the mounting panel 30. The eX- ternal end 32 of shaft 24 has secured thereto a knob 33 by means of which the shaft may a The peripheral edge of the washer is castel-- 'Y lated or serrated as indicated at 36. Also, ether-washer has a depressed or concave shape as isobvious in Fig. 6. Furthermore, the ,washer is provided with a lateral .extension I lor arm 38-which somewhat resembles a U in *14, "shape Lemergetni of this arm Fig. e) is bi- 'furcated as denoted at 39. T e purpose of this forked or bifurcated end 39 will be more fully explained hereinafter.

' `Also mounted on the reduced end 23 of ismost clearly shown in Figs. 1 and 3 and which is claimed in my copending patent ap'- plication Serial No. 114,126, filed June 7, 1926. This assembly includes a contact arm 46 having anfarcuate shaped mounting portion 47. The base or mounting portion 47 is provided with an arcuate slot 48 so as to pro- K 06 24, This collar 52 is suitably clamped to the sleeve includes a threaded opening 21 and shaft^24 is a contactarm assembly 45 which portion 49 which is ada ted to be flexed into and out of the plan o the base 47. A set screw 56 serves to secure the collar 52 to the end 23 of the shaft. The slot 48 in the base 47 provides the offset portion 49 with sufcient resiliency to enable it to urge the contact arm into engagement with the resistance wire or winding of the resistant strip designated generally by the reference characv "Obviously, when the contact arm assembly is mounted on the end 23 of the operating shaft abutting the resilient washer 35, the washer 35 not only serves as a resilient mount ing for the assembly but also serves as a 30 universal mountin due to its arcuate and depressed shape. v uch -an arrangement insures a smooth movement on the part `of the contact arm surrounding its entire range of movement. Then, too, it should be noted that with the exception of the contact portion the entire contactarm assembly 45 is disposed 4in the depressed portion 17 of the base l5within the dimensions of the base thus permitting of a very compact piece of' electrical apparatus.

The resistant strip'60 comprises an insulator or core 61 having wound thereon a plurality of windings of resistance wire 62. This resistance may be made in accordance with the winding process disclosed in the copending patent application of Charles Havlish,`Serial Np. 729,479, filed August 1, 1924,

contact portionv 50 of arm 46. The base 15 has. formed integral therewith a pair of stops 65 and 66 (Fig. 7) which serves to limit the travel of the contact arm 46. To the best of my knowledge I am the first to form the. stops integral With themain portion of the body; both the stops and the main portion of the body comprising or rather being part of the vsame molded product.

Now, it will be evident from Figs. 1 and 2 that the corrugations of the corrugated flange 64 ali n with the corrugations 16 of the body 15. heydiameter ofthe corrugated flange is just enough larger than the diameter of the corrugated body 15 to enable it to accommodate the resistance strip 60 when the same is disposed about the-base 15. The ilange has aslightly irregular 'portion- 70 which cooperates with the fastening bolts used tose- M cure the resistance strip to the base 15. The portion of 'the body 15 adjacent the irregular portion 70 f the flange 64 is not 130 corrugated as is evident from Fig. 4. I have designated this uncorrugated section of the body by thev reference character 71. The previously described stops ,65 and 66 are formed integral with this portion 71. Now the section or portion 71 has a pair of elongated apertures 73 and 74 which communicate with apertures 75 and 76 in portion 70 of the flange (Fig. 2). The apertures or openings 73 and 75 are adapted to receive a square headed screwv 77 and the apertures or openings 74 and 76 are adapted to receive a square headed screw 78. By providing the openings 75 and 76 it is possible to insert the Shanks of the associated screws expediently and with facility into slots or apertures 73 and 74.

Now when the two screws or bolts 77 and 78 are in their proper position they will both be substantially parallel to the panel 3() as is obvious from Fig. 3. Screw 77 has a square head 79 and screw 78 has a. square head .8O which are adapted to be locked in position within the hollow or opening 19 of the base 15. The depressed or concave portion 17 of the base has a pair of tapered or slanting surfaces 81 and 82 adapted to cooperate with the heads 79 and 80 of the previously mentioned bolts (Fig. 4). These surfaces 81 and 82 taper outwardly towards the periphery of the base 15. The tapering surface 82 is illustrated in F ig. 3 and tapering surface 81 is substantially like the surface 82. The surface 81 terminates in a pocket or seat 83 for the screw head 79 and the surface 82 terminates in a pocket or seat 84 for the screw head 80. Pocket 83 is defined by a pair of projections 85 and 86 formed integral with the depressed portion 17 of the base. On the other hand pocket 84 is defined by the projections 86 and 87 formed integral with the base. The tapered surfaces 81 and 82 permit the screw heads 79 and 80 to all times slide into their respective pockets 83 and 84 upon the insertion of the screws 77 and 78 into their respective apertures in the section 71 of the base. Also the projections 85, 86 and 87 cooperate to prevent rotation of the screws. In other words, the screws are anchored against rotation by means formed integral with the molded base 15.

The shank of screw or bolt 77 is adapted to extend through an aperture 89 at one end of the strip 61 of resistance strip 60 and the shank of screw or bolt 78 is adapted to extend through an aperture 90 in the other end of the resistance strip 61. The two bolts cooperate to securely clamp the resista-nce strip about the corrugated periphery of the base 15. The resistance wire 62 extends clear up to the shank of bolt 77 and has its end bent into a hook 89 which embraces the shank of the bolt.. A washer 91 is disposed on top of this hooked end 89 and a pair of locknuts 92 and 93 threaded upon the external end of the bolt 77 serves to securely clamp the assol ciated end of the resistance strip to the base and at the same time serves to insure a good electrical connection between the resistance and the bolt 77. The bolt 77 can be connected in any desirable manner to one end 0f an electrical circuit.

`The resistance wire 62 does not extend clear up to the shank of'bolt 77 as is obvious in Fig. 4. A pair of washers 95 and 96 encircle the free end of the bolt 78 and a pair of locknuts 97 and 98 serve to securely clamp the washers to the associated end of the resistance 60, thus clamping the resistance to the base.

Alsothe bolt 78 may be connected in any,4 desirable manner to another end of the preaperture 99 in the depressed portion 17 ofy the base which aperture communicates with pocket 84 associated with the head 80 of the bolt 78. The bifurcated end 39 of the arm 38 'extends through this aperture 99 into the pocket 84 and straddles the shank of lbolt 7 8. The head 80 of the bolt 78 is adapted to securely clamp this bifurcated end 39 to the associated portion of the base l5. Thus it will be apparent that the arm 38 of the washer performs'two functions, namely, that of anchoring the washer against rotation and that of establishing an electrical connection between the contact arm mechanism 45 and the terminal bolt 78.

The operation of my novel current control device is believed to be obvious from the foregoing detailed description. By turning the knob 33 the contact mechanism 45 can be rotated to vary the point of contact -between the arm 46 and the resistance 62 of the strip 60. The resilent washer 35 not only provides a universal and resilient mounting for the contact mechanism but also serves to establish anelectrical connection between one of the terminal bolts and the contact mechanism. Furthermore, due to the fact that the base 15 is of a molded composition the same may be very economically manufactured.

In Figs. 9, 10, 11 and 12 I have illustrated somewhat diagrammatically a form of resistance strip 60 which may be used in place of the resistance strip 60. This strip 60 comprises essentially an insulator corev 61 having wound thereon a resistance wire 62.v This wire 62 is suitablyanchored at each end to the core 61. In this form of strip the core 61 need not be provided with grooves for receiving the individual windings on the Strip.

winding machine. The resistance wire 62 is preferably provided with insulation such as a coating of black enamel 63. By using black enameled wire it is possible to wind the p latter pocket serving to secure said exten- Istrip with the individual turns in contact with each other.

In order to provide a contact surface for -thecontact arm of the device to engage, I

preferably file one edge 64 of the resistance strip 60 to bare the resistance wire 62:I of the black enamel insulation 63 at this point. By baring the insulation at 64 I provide a contact surface which extends the length of the strip without at the same time interfering with the insulation between the individual turns of the wire on the strip.

Now I ,desire it understood, although I have illustrated anddescribed in detail the preferred embodiments of my invention, the invention is not to be thus limited but only insofar ldefined by the scope and spirit of the appended claims.

I claim:

1. In combination, a rheostatv base of molded composition having its periphery corrugated, resistance means comprising a core encircling the periphery of the molded base and a resistance elementv wound upon said core and also encircling said base, the depressed portions of the corrugations opening directly acrom' the periphery of the base to form transverse'channels across the periphery of the base from one side of the resistance `means to the other and between the resistance element and the molded base for cooling pury poses.

2. In an electric current control device, a base of molded composition substantially arcuate in shape and having a corrugated outer periphery resistance means wound about an annular axis encircling the eriphery of the niolded -base and disposed wliolly outside the peaks of the corrugations, the depressed portions of the corrugations opening directly across the periphery of the base to form transverse channels 'across thev periphery of the baseA from one side to the other between the resistance selement and the molded base for cooling purposes.

said concave end having a plurality of-pock-4 ets communicating with the slots in said rim, said pockets receiving portions of said fas'- tening members to lock them against rotation, said" contact mechanism including a reseau' spring washer disposed on said depressed end comprising a metallic flange having a lateral extension projecting through an opening y in said depressed end into one of said pockets,

the fastening member associated with said 4 S n c sion to said base to prevent rotatlon of sald washer.

4. In an electric 'current control device, a

base of molded composition comprising a cup having an annular rmi, a concaveend, and

radially extending corrugations normal tosaid concave end, a resistance element disposed about the said corrugated rim and contact mechanism mounted on said end for cooperating with saidresistance element, said mechanism including a spring washer having a lateral arm extending through a slot in said concave end and fastened to said rim.

.5. In an electric current control device, a.

base of molded composition comprising a cup having a corrugated annular rim and a concave end, a resistance element disposed about the peaks of the corrugations in said rim and contact mechanism mounted on said end for cooperating with said resistance element,`

said mechanism including a springwasher having a lateral arm fastened to said base.

sov

6. In combination, a cylindrical insulating base having its periphery corrugated, and a resistance unit comprislng a core encircling.

the outer peaks of the corrugations with a resistance element mounted upon said core y and bridging air passages beneath the resistance unit for cooling purposes. p

7. In combination, a cylindrical insulating Abase .having its periphery corrugated, and

a resistance unit encircling the periphery of the base and comprising a core havlng a resistance element wound thereupon, the corrugations in the periphery of the insulating base opening transversely across said base and disposed internally of the inner periphery of said resistance unit for-cooling purposes. I

8. In an electric current control device of molded composition comprising a cylindrical base member with an external shoulder thereon, the periphery of the base member lhaving' Vcorrugations traversing it from one side to' the other including .the shoulder, va resistance 'means comprising a core with a resistance element wound-.thereon disposed about the peaks of the corrugations of the base member having one edge abutting the corrugated shoulder and the other edgeoverhanging the edge of said base, said corrugations on the base member and shoulder providing a means l for air cooling both. the windings on thegin-` ner periphery of the resistance unit and the of lsaid base member. A

9. In an electric current control device of molded composition comprising a cylindrical base having transverse ridges across its pev windings on the edge abutting the shoulder Y riphery, said ridges having projections thereon, a resistance means comprising a core with a resistance element Wound thereablout supported on said ridges abutting the projections thereon capable of being cooled on all sides by disposition of its outer periphery and one edge thereof to the air and by the disposition of its inner periphery'and other edge to the air between the ridges on the cylindrical base. In witness whereof, I hereunto subscribe my name this 18th day of October, 1926. NEWTON C. SCHELLENGER 

